rails 从片段缓存中遗漏了一些部分

Question

我有一个使用 pundit gem 进行授权的 rails 4 应用程序。如果我像下面的代码那样做俄罗斯娃娃片段缓存，用于授权的条件语句也会被缓存，这不好，因为编辑/删除按钮应该只对post.user可用。

解决这个问题的好方法是什么？我应该将缓存分成更小的部分还是有办法排除缓存的某些部分？在这种情况下，rails 约定是什么？

index.html.erb

<% cache ["posts-index", @posts.map(&:id), @posts.map(&:updated_at).max, @posts.map {|post| post.user.profile.updated_at}.max] do %>
  <%= render @posts %>
<% end %>

_post.html.erb

<% cache ['post', post, post.user.profile ] do %>

  <div class="row>
    <div class="col-md-2">
      <%= link_to user_path(post.user) do %>
        <%= image_tag post.user.avatar.url(:base_thumb), class: 'post-avatar' %>
      <% end %>
    </div>

    <div class="col-md-8">
      <span class="post-user-name"><%= post.user.full_name %></span>
      <span class="post-updated"><%= local_time_ago(post.updated_at) %></span>
      <div class="post-body">
        <%= post.body %>
      </div>

    <div class="col-md-2" style="text-align:right;">

      <!--############### THIS IS THE PART THAT SHOULD NOT BE CACHED #############-->

      <% if policy(post).edit? && policy(post).delete? %> 
        <li class="dropdown">
          <ul class = "dropdown-menu dropdown-menu-right">
            <li>
              <%= link_to "Edit Post", edit_post_path(post), remote: true, type: "button", 'data-toggle' => "modal", 'data-target' => "#updatepost_#{post.id}" %>
            </li>   
            <li>
              <a href="#" data-toggle="modal" role="button" data-target="#deletepost_<%= post.id %>">Delete Post</a>
            </li>
          </ul>
        </li>
      <% end %>

      <!--########################## UNTIL HERE ############################-->

    </div>
  </div>

  <div class = "row comment-top-row" style="padding-bottom:10px;">
    <div class="col-md-12 post-comment-form">
      <%= render partial: 'posts/post_comments/post_comment_form', locals: { post: post } %>
    </div>
  </div>

  <div class = "row">
    <div class="col-md-12 post-comment-insert-<%= post.id%>">
      <%= render partial: 'posts/post_comments/post_comment', collection: post.post_comments.ordered.included, as: :post_comment, locals: {post: post} %>
    </div>
  </div>

  <% if policy(post).edit? %>
    <div class="modal fade updatepost" id="updatepost_<%= post.id %>" tabindex="-1" role="dialog" aria-labelledby="myModalLabel">
       <!-- FORM GETS RENDERED HERE VIA JS -->
    </div>
  <% end %>

  <% if policy(post).delete? %>
    <div class="modal fade" id="deletepost_<%= post.id %>" tabindex="-1" role="dialog" aria-labelledby="myModalLabel">
      ......
    </div>
  <% end %>

<% end %>

Answer 1

Russian Doll Caching 是一种简单但方便的缓存方式，没有复杂的选项或约定可以从中排除部分片段。除此之外，它更多地与缓存策略有关。以下是针对这种用户特定情况的两种策略：

1. 单独重新排列并手动缓存片段，我不建议这样做。因为它更复杂并且没有利用俄罗斯娃娃缓存的优势。也不那么可维护。这是一个例子：

index.html.erb

<% # pull out cache %>
<%= render @posts %>

_post.html.erb

<% cache post %>
  <%= # first part %>
<% end %>

<% # without cache %>
<%= # user specific part %>

<% cache post %>
  <%= # third part %>
<% end %>

1. 首选方式：将current_user 添加为cache_key 的一部分，这意味着您将拥有与您的用户一样多的片段缓存，并且每当帖子或用户更改指纹时片段将自动失效。这更加优雅和可维护。这是一个例子：

index.html.erb

<% cache ["posts-index", @posts.map(&:id), @posts.map(&:updated_at).max, @posts.map {|post| post.user.profile.updated_at}.max] do %>
  <%= render @posts %>
<% end %>

_post.html.erb

<% cache ['post', post, post.user.profile, current_user ] do %>
  <div class="row>
    <div class="col-md-2">
      <%= link_to user_path(post.user) do %>
        <%= image_tag post.user.avatar.url(:base_thumb), class: 'post-avatar' %>
      <% end %>
    </div>

    <div class="col-md-8">
      <span class="post-user-name"><%= post.user.full_name %></span>
      <span class="post-updated"><%= local_time_ago(post.updated_at) %></span>
      <div class="post-body">
        <%= post.body %>
      </div>

    <div class="col-md-2" style="text-align:right;">
      <% if policy(post).edit? && policy(post).delete? %> 
        <li class="dropdown">
          <ul class = "dropdown-menu dropdown-menu-right">
            <li>
              <%= link_to "Edit Post", edit_post_path(post), remote: true, type: "button", 'data-toggle' => "modal", 'data-target' => "#updatepost_#{post.id}" %>
            </li>   
            <li>
              <a href="#" data-toggle="modal" role="button" data-target="#deletepost_<%= post.id %>">Delete Post</a>
            </li>
          </ul>
        </li>
      <% end %>
    </div>
  </div>

  <div class = "row comment-top-row" style="padding-bottom:10px;">
    <div class="col-md-12 post-comment-form">
      <%= render partial: 'posts/post_comments/post_comment_form', locals: { post: post } %>
    </div>
  </div>

  <div class = "row">
    <div class="col-md-12 post-comment-insert-<%= post.id%>">
      <%= render partial: 'posts/post_comments/post_comment', collection: post.post_comments.ordered.included, as: :post_comment, locals: {post: post} %>
    </div>
  </div>

  <% if policy(post).edit? %>
    <div class="modal fade updatepost" id="updatepost_<%= post.id %>" tabindex="-1" role="dialog" aria-labelledby="myModalLabel">
       <!-- FORM GETS RENDERED HERE VIA JS -->
    </div>
  <% end %>

  <% if policy(post).delete? %>
    <div class="modal fade" id="deletepost_<%= post.id %>" tabindex="-1" role="dialog" aria-labelledby="myModalLabel">
      ......
    </div>
  <% end %>
<% end %>